Some of us can’t identify faces to save our lives and some can unhesitatingly identify a long-lost classmate from kindergarten. While science has largely cracked the mysteries of vision – we use our eyes – facial recognition has been confounding, in people at least. “Face” neurons had been found in macaques some 50 years ago, and that’s where the research stayed.
Now, for the first time an Israeli-French team of scientists has identified specific neurons that fire madly when shown a face but not a barn or shoehorn. These nerve cells lie, suitably, within the “facial recognition system” in our brain.
Or at least the scientists found the neurons right where they’d been expected in the one person they tested, says Dr. Vadim Axelrod, head of the Consciousness and Cognition Laboratory at Bar-Ilan University, in collaboration with a team from the ICM Brain and Spine Institute and Pitié-Salpêtrière Hospital led by Prof. Lionel Naccache, in a study published Monday in Neurology.
Wait, how did they come to test this person? Conveniently, the specimen had micro-electrodes implanted in the vicinity of the fusiform face area (FFA) the largest and probably most important face-selective region of the human brain, Axelrod explains.
The neurons within said specimen’s FFA responded much more strongly to faces than to city landscapes or objects, the team reported.
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Pressed to explain whether they had identified a domain (tens of thousands of cells) in the FFA or actual specific neurons, Axelrod explains that it’s neurons – individual nerve cells.
Come on, not with Brad Pitt
One might assume that neurons in the vicinity of the fusiform would respond more to faces than to landscapes. But this was the first actual proof in people. Or person.
It also bears noting that the specimen’s fusiform nerves responded similarly to all faces, familiar and unfamiliar, and did it fast: A strong response could be observed within 150 milliseconds of showing the image.
A different facial-recognition area within the medial temporal lobe, called the “Jennifer Aniston cells,” also responds to faces – of celebrities – and takes twice as long.
“For example, a neuron of one patient responded almost solely to different pictures of Bill Clinton,” Rodrigo Quiroga and colleagues reported in Nature in 2005. Pictures of Jennifer Aniston triggered a single neuron in the medial temporal lobe in another person – but pictures with her ex, Brad Pitt, left that cell clammy. Well, different strokes for different folks and their facial recognition cells.
Yet another cell in that 2005 study reacted when shown an episode of the TV cartoon “The Simpsons,” but it might have reacted to other things too if shown them, the scientists postulate.
OK, we got that the fusiform neurons see “face.” But what do they actually do, in Axelrod’s opinion, given that they react the same to pictures of Clinton, Aniston and your dog? Who knows, but Axelrod suggests they might act as face detectors (“Think about Facebook, which detects faces on the picture – we also need something of this sort in our brain”).
Maybe these neurons can discriminate between people, he says. “For example, in one of my previous fMRI studies, I showed that [brain areas] could discriminate between different images of Shimon Peres and Benjamin Netanyahu. In this present study, we could not test face recognition because we recorded several neurons only. But this cannot be ruled out.”
Finally, how valid is Axelrod’s 2019 research done on this rather small sample (one) to the generality of humankind? Do we all have the same neurons? Sort of.
“The word ‘same’ is a bit misleading because there are no two identical neurons, like there are no two identical leaves on a tree,” Axelrod says. “But in general, yes, all people should have such neurons. In the past, using fMRI I personally scanned hundreds of participants and there was no single participant without a face-region in the visual cortex [the fusiform face area]. So, we all likely have neurons in the visual cortex that respond to faces.”
Axelrod acknowledges that the sample size cannot be representative of humanity as a whole, and also notes that his specimen didn’t suffer from prosopagnosia. “Some researchers think that the reason for their impairment might be related to abnormal connectivity between regions. Anyway, in our study the participant did not have problems with recognizing faces,” he says.